1 files changed, 80 insertions, 0 deletions
diff --git a/src/gen/protoc_insertion_point.rs b/src/gen/protoc_insertion_point.rs
new file mode 100644
index 0000000..0083215
--- /dev/null
+++ b/src/gen/protoc_insertion_point.rs
@@ -0,0 +1,80 @@
+use protobuf::reflect::EnumDescriptor;
+use protobuf::reflect::EnumValueDescriptor;
+use protobuf::reflect::FieldDescriptor;
+use protobuf::reflect::MessageDescriptor;
+use protobuf::reflect::OneofDescriptor;
+
+use crate::gen::code_writer::CodeWriter;
+use crate::Customize;
+
+/// Write `// @protoc_insertion_point(...)` before the element.
+///
+/// This is similar to what `protoc` codegen does for C++ or Java.
+/// This can be used to modify the generated code.
+fn write_protoc_insertion_point(w: &mut CodeWriter, customize: &Customize, arg: &str) {
+    for line in customize.before.iter().flat_map(|s| s.lines()) {
+        w.write_line(line);
+    }
+    w.comment(&format!("@@protoc_insertion_point({})", arg));
+}
+
+pub(crate) fn write_protoc_insertion_point_for_message(
+    w: &mut CodeWriter,
+    customize: &Customize,
+    message: &MessageDescriptor,
+) {
+    write_protoc_insertion_point(w, customize, &format!("message:{}", message.full_name()));
+}
+
+pub(crate) fn write_protoc_insertion_point_for_field(
+    w: &mut CodeWriter,
+    customize: &Customize,
+    field: &FieldDescriptor,
+) {
+    write_protoc_insertion_point(w, customize, &format!("field:{}", field.full_name()));
+}
+
+pub(crate) fn write_protoc_insertion_point_for_special_field(
+    w: &mut CodeWriter,
+    customize: &Customize,
+    message: &MessageDescriptor,
+    field: &str,
+) {
+    write_protoc_insertion_point(
+        w,
+        customize,
+        &format!("special_field:{}.{}", message.full_name(), field),
+    );
+}
+
+pub(crate) fn write_protoc_insertion_point_for_enum(
+    w: &mut CodeWriter,
+    customize: &Customize,
+    enumeration: &EnumDescriptor,
+) {
+    write_protoc_insertion_point(w, customize, &format!("enum:{}", enumeration.full_name()));
+}
+
+pub(crate) fn write_protoc_insertion_point_for_enum_value(
+    w: &mut CodeWriter,
+    customize: &Customize,
+    value: &EnumValueDescriptor,
+) {
+    write_protoc_insertion_point(w, customize, &format!("enum_value:{}", value.full_name()));
+}
+
+pub(crate) fn write_protoc_insertion_point_for_oneof(
+    w: &mut CodeWriter,
+    customize: &Customize,
+    oneof: &OneofDescriptor,
+) {
+    write_protoc_insertion_point(w, customize, &format!("oneof:{}", oneof.full_name()));
+}
+
+pub(crate) fn write_protoc_insertion_point_for_oneof_field(
+    w: &mut CodeWriter,
+    customize: &Customize,
+    field: &FieldDescriptor,
+) {
+    write_protoc_insertion_point(w, customize, &format!("oneof_field:{}", field.full_name()));
+}